TEREDO. 
113 
however to be no more reason for classing these 
shells with the multivalves, than Turbines and 
others, which possess an operculum, with the 
bivalves. The only difference between the lid of 
the Teredo and that of a Turbo is, that the one is 
constructed of four pieces, the other of a single 
disk. These pieces cannot constitute the shell, 
because the animal cannot be said to inhabit them, 
as it does the testaceous tube. Neither is there 
any analogy between them and the accessary 
valves of Pholas. 
At first sight, the Teredo may easily be mistaken 
for a Serpula, and in many cabinet specimens the 
valves are lost. There are, however, but three spe- 
cies of the former genus at present known, and 
their external characters are soon to be dis- 
tinguished. The first, T, navalis, which is the 
most common, is much more thin and brittle than 
Serpulse in general, especially towards the smaller 
end. ’ 
The name Teredo, or is derived from 
rs^sco, to bore, and is sufficiently descriptive of the 
mode in which all the species effect their settle- 
ment. 
I 
